Temper
Definition
Material deliberately added to clay before forming to reduce drying shrinkage and firing cracking; common temper types include sand, grog (crushed old pottery), shell, volcanic ash, and organic material. Temper choice varies regionally and culturally.
- Purpose
- Reduces drying shrinkage and firing cracks
- Common materials
- Sand, grog, shell, volcanic ash, organic matter
- Study method
- Thin-section petrography under polarised light
- Forensic use
- Sourcing and cultural attribution of ceramic evidence
Common questions
How is temper identified in a lab?+
A thin section of the fired sherd is cut and examined under a petrographic microscope, where mineral grains and inclusions show diagnostic colour, cleavage and extinction patterns that separate sand from grog, shell or volcanic material.
Why does temper matter to a forensic case?+
Because temper choice is regional and cultural, matching the temper in a questioned ceramic fragment to a known production source can support or rule out a claimed origin, similar to how soil or glass comparisons work in trace evidence.
Related terms
- Ceramic Fabric
- The combination of clay matrix and included particles (temper, natural inclusions, and voids) that makes up a fired ceramic; the raw material...
- Dehydroxylation
- The loss of structural hydroxyl groups from clay minerals (principally kaolinite) between about 450 and 600 °C during firing; an irreversible reaction...
- Grog
- Crushed fragments of previously fired ceramic mixed into new clay as temper; recognisable in thin section by their fired-clay texture, which differs...
- Mullite
- An aluminosilicate phase (3Al2O3·2SiO2) that nucleates in fired clay above roughly 980 °C, coinciding with the characteristic exothermic reaction of the kaolinite-to-mullite...
- Provenance
- The documented origin of a media file: the device that captured it, the time and location of capture, the chain of custody...